Lubricating oil compositions are often prepared by blending additive concentrates containing one or more performance improving additives into an oil of lubricating viscosity. Additive concentrates are "packages" containing one or more performance improving additives. While it has been noted that from time to time chemical interactions take place between two or more components in additive concentrates, sometimes leading to unexpectedly improved performance, the usual reason for supplying additives in the form of additive concentrates is economics.
Often, the manufacturer of lubricating oil compositions does not manufacture the performance improving additives, or manufactures additives at a location remote from the plant where the lubricating oil composition is blended. Accordingly, it is usually necessary to transport the additives to the lubricating oil plant. Economics dictates that the additives be supplied in as concentrated a form as possible in order to keep shipping and storage costs to a minimum. It is also convenient to provide additives from a single package containing more than one component rather than to provide a number of additives individually.
At the lubricant blending site, convenience and economics are also considerations. It is convenient for the lubricant manufacturer to incorporate additives from a single package rather than individually. Moreover, when additives are supplied from a package, storage and supply facilities are reduced in number, resulting in improved economics.
As noted hereinabove, additives making up an additive concentrate may interact in a beneficial manner. From time-to-time, the interactions are adverse, for example, the interaction may result in diminished performance, or the additives may be physically incompatible, resulting in a non-homogeneous mixture. The present invention relates to the latter set of circumstances, i.e., where additives are mutually incompatible resulting in non-homogeneous mixtures.
Automatic transmission fluids (ATF) are well known in the art. In general, however, automatic transmission suppliers and manufacturers specify performance characteristics of the transmission operating with a fluid rather than fluid composition for use in the transmission. It is then up to fluid providers to formulate fluids which meet performance characteristics. Recently, performance requirements for ATF Service Fills have become more stringent with publication of DEXRON.RTM.-III ATF Specification by General Motors, GM 6297M, April, 1993. The Specification is available from General Motors, Material Engineering Transmissions, M/C 748 Ypsilanti, Mich. 48197 and is herein incorporated by reference.
In general, automatic transmission fluids comprise a base oil and additives. The base oil may be from natural sources, mineral and plant oils, and from synthetics and will be of the proper viscosity for their intended use. Additives are then incorporated into the base oil with those incorporated being dependent upon the properties that the fluid formulator is striving for. Additives for ATF include the following:
______________________________________ anti-oxidants viscosity improvers corrosion inhibitors friction modifiers rust inhibitors defoamers anti-wear agents pour point depressants dispersants detergents seal swell agents ______________________________________
Formulations for ATFs and functional fluids containing some or all of the above additives in a select base oil are freely available in the patent literature. For instance, U.S. Pat. No. 4,209,587 to Koch lists lubricating/functional fluid compositions with various combinations of base oils and additives. U.S. Pat. No. 5,344,579 to Ohtani and Harley describes a friction modifier system for AT and cites additive components for ATFs and their typical ranges. The disclosure of both U.S. patents cited above are herein incorporated by reference. It must be noted that the lines between chemically active and inactive additives are not so distinct. Also, additives may well be multifunctional and are categorized above only for the sake of convenience.
One of the major requirements for automatic transmission fluids has been improved low temperature performance as demonstrated by a maximum Brookfield viscosity of 20,000 centipoise at -40.degree. C. The viscosity modifier, which can comprise nearly 50 weight percent of the total additive system employed in an automatic transmission fluid can have a major impact on the low temperature performance. Such characteristics are also desirable in other applications such as in gear lubricants. The copolymers of this invention are also useful in many other lubricating oil compositions including, but not limited to engine oils, hydraulic oils, industrial oils, etc.
Recently, the trend has been in the direction of lubricants that retain their viscosity characteristics during use. For lubricating oils and particularly for mineral oil based lubricating compositions, improved viscosity characteristics are imparted by the use of viscosity improvers which arc usually polymeric materials. In order to maintain viscosity characteristics during use, a lubricating composition must contain a polymeric viscosity improver that resists shearing, that is, loss of molecular weight when the lubricant is subjected to high mechanical shear conditions.
Shear resistant polymers tend to be lower molecular weight polymers. In order to obtain desired viscosity improving characteristics, with these lower molecular weight, shear stable, polymeric viscosity improvers, they are generally used in increased amounts compared to higher molecular weight polymers. When these lower molecular weight viscosity improvers are combined with traditional, higher molecular weight additives, especially ashless dispersants, incompatibility and separation result.
Another requirement is that the automatic transmission fluid contains additives that prevent or reduce the deposition of sludge and varnish deposits.
Compositions that provide these desirable benefits frequently are additive concentrates that contain dispersants and viscosity improvers. Under certain circumstances, these ingredients are mutually incompatible, resulting in non-homogeneous compositions.
Dishong, et al in U.S. Pat. No. 5,157,088 teaches nitrogen-containing esters of carboxy-containing interpolymers wherein the interpolymer has inherent viscosity of from about 0.05 to about 0.30 may be used in lubricants and additive concentrates together with other known additives including, inter alia, dispersants.
Bloch, et al in U.S. Pat. No. 5,641,732 teaches partial synthetic automatic transmission fluids containing a mixed basestock containing synthetic oil and natural oil, a viscosity improver, including hydrocarbyl polymers and polyesters having moleculair weight ranging from 50,000 to less than 175,000, and any of a wide variety of friction modifiers, including reaction product of aliphatic hydrocarbon substituted carboxylic acids/anhydrides, where the substituent contains from 9 to 29 carbon atoms with polyamines.
Tipton in U.S. Pat. No. 5,620,948 teaches additive combinations containing a Mannich dispersant having base no in range of from about 45 to about 90, a boron compound, and an organic phosphorus acid, ester or derivative, and optionally, a thiocarbamate and a nitrogen containing ester of a carboxy containing interpolymer.
Pennewiss, et al in U.S. Pat. No. 4,867,894 describes polymethacrylate copolymers, optionally containing groups derived from nitrogen-containing monomers useful as pour point depressants in petroleum oils.
Cusano, et al in U.S. Pat. No. 4,146,492 describes a lubricating oil composition comprising a lubricating oil, a pour depressant polyalkylacrylate as described therein, a viscosity improving ethylene-propylene copolymer of molecular weight between about 10,000 and 150,000, and any of a wide variety of supplementary additives including ashless dispersants such as alkenyl succinimides, e.g., polyisobutylene (700-2000 m.w.) succinimide derived from tetraethylene pentamine.
Coleman in U.S. Pat. No. 4,374,034 describes compositions prepared by polymerizing under free radical conditions, at least one ethylenically unsaturated monomer in the presence of at least one oil-soluble dispersant characterized by the presence of an oil solubilizing group containing at least about 30 carbon atoms and a polar group bonded thereon.
It is a principal object of this invention to provide homogeneous additive concentrates.
It is a particular object of this invention to provide homogeneous additive concentrates comprising polymeric ester viscosity improvers and hydrocarbyl group substituted ashless dispersants.
Other objects will in part be obvious in view of this disclosure and will in part appear hereinafter.